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A method of forming a ring gear from a ring blank includes providing a
mandrel having a central axis and an outer annular forming surface. The
outer annular forming surface defines a plurality of forming elements
having a forming element axis offset from the central axis of the
mandrel. The ring blank has a ring axis and is placed over the mandrel
generally aligning the central axis of the mandrel with the ring axis of
the ring blank. A roll is provided having a roll axis that is generally
parallel with the element axis. The roll is forced radially inwardly
while circumscribing the central axis. The roll pivots around the roll
axis deforming the ring blank radially inwardly forming teeth on an inner
surface of the ring blank that coaxial with the element axis and offset
from the mandrel axis.

1. A method of forming a ring gear from a ring blank, comprising the steps of: providing a mandrel having a central axis and an outer forming surface defining a plurality of
forming elements each forming element having a forming element axis offset from the central axis of the mandrel; placing the ring blank having a ring axis over the mandrel and generally aligning the central axis of the mandrel with the ring axis of the
ring blank; providing a roll having a roll axis being generally parallel with the forming element axis of the forming element interposed between the roll and the mandrel central axis; and forcing the roll radially inwardly relative to the mandrel
central axis and circumscribing the mandrel central axis while rotating the roll about the roll axis thereby deforming the ring blank radially inwardly and forming a plurality of teeth with each tooth being spaced from the adjacent tooth on an inner
surface of the ring blank, the formed tooth being substantially parallel with the forming element axis and angularly offset from the mandrel central axis.

2. The method set forth in claim 1, wherein said step of circumscribing the mandrel central axis is further defined by rotating the mandrel while forcing the roll radially inwardly relative to the mandrel central axis.

3. The method set forth in claim 1, further including the step of articulating the roll in a direction generally parallel to the mandrel central axis while forcing the roll radially inwardly relative to the mandrel central axis.

4. The method set forth in claim 3, wherein said step of articulating the roll in a direction generally parallel to the mandrel central axis while forcing the roll radially inwardly is further defined by articulating the roll the full extent of
the ring blank.

5. The method set forth in claim 1, wherein said step of providing a roll is further defined by providing a plurality of wheels circumferentially spaced around the mandrel.

6. The method set forth in claim 1, wherein said step of providing forming elements is further defined by providing helical ribs on the outer forming surface of the mandrel.

7. The method set forth in claim 1, wherein said step of deforming the ring blank radially inwardly is further defined by decreasing an outer diameter of the ring blank by forcing the ring blank over and between the forming elements.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to methods of forming a ring gear. More specifically, this invention relates to methods of forming a ring gear having internal teeth without the use of machining operations.

Gears are widely used in the mechanical arts to transfer motive force between mechanical components. The gear typically includes gear teeth that engage teeth formed on a cooperable gear or mechanical device to transfer motive force between the
two elements. Because the mechanical forces are substantial upon each of the gear teeth, a precise dimensional configuration or profile is required to provide a uniform engagement. This is particularly necessary for gears used in automotive
transmissions. To achieve precise dimensional configuration, milling, broaching, and machining operations are generally performed on a gear blank to achieve necessary gear teeth profiles. Generally, teeth formations may be formed in the gear blank and
then a subsequent machining operation is performed to provide precise dimensional characteristics necessary to withstand the high loads required of complex motive operations used, for example, in automotive transmissions.

Attempts have been made to cold work or flow form gear teeth profiles in simple gears starting from a blank without the use of additional machining operations. While flow forming and cold working have shown promise in eliminating the necessary
machining operations, forming defects are prevalent, have heretofore reduced the ability to use gears having teeth formed only by cold working or flow forming in transmission operations. For example, a gear having angular or slightly helical teeth not
parallel to a ring axis that have been formed by cold working or flow forming is known to have inconsistencies resulting from not fully filling mandrel formation elements used to form the gear teeth. Inconsistent forming of the gear teeth in a cold
working or flow forming process results in mechanical failures in devices in which the gears are used. Thus, it has been necessary to machine gear teeth used in high speed high torque operations.

Therefore, it would be desirable to provide a method of forming defect-free gear teeth on a gear blank that does not require a secondary machining operation, yet enables the resultant gear to be used in a high speed high torque mechanical
device.

SUMMARY OF THE INVENTION

The present application discloses a method of forming a ring gear from a ring blank. A mandrel having a central axis and an outer annular forming surface defines a plurality of forming elements each having a forming element axis that is offset
relative to the central axis of the mandrel. The ring blank has a ring axis and is placed over the mandrel, generally aligning the central axis of the mandrel with the ring axis of the blank. A roll having a roll axis that is generally parallel with
the forming element axis located between the central and roll axes is forced radially inwardly relative to the central axis while circumscribing the central axis. The roll rotates about the roll axis while being forced radially inwardly relative to the
central axis, and deforms the ring blank radially inwardly toward the central axis, forming teeth on an inner surface of the ring blank that are parallel with the forming element axes and offset relative to the mandrel central axis.

Prior art flow forming techniques have used deformation devices that deform the ring blank over a mandrel or forming device configured to form gear teeth on the ring blank. Typically the device is a roll having an axis of rotation that is
angularly aligned with the mandrel central axis regardless of whether the gear teeth are to be angularly aligned with the mandrel central axis. This results in inconsistency in the teeth formed in the gear blank because the forces necessary to deform
the ring blank into the forming elements are not uniform. It has been determined by the Applicant that aligning the axis of the roll in a parallel relationship with the axis of forming element over which the roll is superposed and not with the mandrel
central axis overcomes this deficiency in prior art flow forming techniques. This alignment allows for the complete elimination of any subsequent or secondary machining operations required to provide uniform, dimensionally accurate teeth on the ring
gear.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with accompanying drawings, wherein:

FIG. 1 is a schematic representation of a partial plan view of the inventive flow forming method;

FIG. 2 is partial sectional view along line 2-2 of FIG. 1 showing a ring blank interacting with a mandrel forming element;

FIG. 3 is a partial sectional view along line 3-3 of FIG. 1, showing the ring blank being deformed radially inwardly relative to the mandrel central axis, and over and between the forming elements of the mandrel;

FIG. 4 is a schematic elevational view of the roll of the present invention deforming the ring blank radially inwardly;

FIG. 5 is a schematic elevation showing the removal of the formed ring gear from the mandrel; and

FIG. 6 is a plan view along line 6-6 of the ring gear of the present invention shown in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

A schematic plan view of the forming assembly 10 is generally shown in FIG. 1. A mandrel 12 having a central axis a is shown, around which a ring blank 14 is disposed. The ring blank 14 includes an inner annular surface 16 that is smooth, and
a concentric, smooth outer annular surface 17. Initially, ring blank inner and outer walls 16, 17 are cylindrical. The mandrel 12 includes radially inner and outer diameters 23, 24 between which is forming surface 18 that defines a plurality of forming
elements 20. The forming elements 20 are angularly offset from the mandrel axis a as is best represented in FIG. 4 and will be explained further below.

The inner annular surface 16 of the ring blank 14 defines an inner diameter 22 that initially is generally equivalent to outer diameter 24 of mandrel 12 and a first extent of the forming elements 20. Therefore, the ring blank 14 is secured upon
the mandrel 12 with an interference fit between the inner annular surface 16 of the ring blank 14 and the forming elements 20 of the mandrel 12. It should be understood by those skilled in the art that the ring blank 14 and the mandrel 12 have the same
central axis a, or are otherwise coaxial. A roll 26 is mounted upon a drive 28 that provides force in a direction of arrow 30, driving the roll 26 radially inwardly toward mandrel axis a. The roll 26 is preferably a wheel 32 that rotates about roll axis
34 in the direction of arrow 35 along ring blank outer annular wall 17. Preferably, a plurality of rolls 26 or wheels 32 is provided to reduce the cycle time of the ring gear formation.

As shown in FIG. 1, each roll 26 circumscribes the ring blank 14 while being forced radially inwardly by the drive 28 over and between the forming elements 20, reshaping the inner annular surface 16 of the ring blank 14 into a configuration
defined by the forming elements 20 of the mandrel 12. The deformation of the inner annular surface 16 of the ring blank 14 forms gear teeth 36 associated with resulting gear 46 (FIG. 6). By driving the roll 26 radially inwardly relative to mandrel axis
a, the outer diameter of the ring blank 14 is decreased as the gear teeth 36 are formed on the inner annular surface 16. The mandrel 12 rotates about mandrel axis a in the direction of arrow 40 while each roll 26 is forced radially inwardly toward axis
a. Alternatively, the mandrel 12 is stationary while each roll 26 circumscribes the ring blank 14 in a direction of arrow 42. A still further embodiment is contemplated where the mandrel 12 rotates about mandrel axis a in a direction of arrow 40 while
each roll 26 circumscribes the ring blank 14 in an opposite direction of arrow 42, further reducing cycle time.

FIG. 2 shows inner annular surface 16 of the ring blank 14 in an abutting relationship with a radially outermost portion of forming surface 18 located at diameter 24 on a forming element 20 of the mandrel 12, prior to forming gear teeth 36.
FIG. 3 shows the ring blank 14 being deformed radially inwardly relative to axis a and over the forming element 20 of the mandrel 12 located between roll axis 34 and mandrel axis a, resulting in gear teeth 36 being formed on the inner annular surface 16
of the ring blank 14. The roll 26 articulates along roll axis 34 in the directions of arrow 50 (FIG. 3) while being forced radially inwardly toward mandrel axis a in the direction of arrow 30 to deform the ring blank 14 radially inwardly relative to
axis a. Roll axis 34 is shown generally parallel to mandrel axis a. Furthermore, the roll 26 moves the full extent of the ring blank 14 so that the entirety of the ring blank 14 is forced radially inwardly to form a uniform outer annular surface 44 of a
formed ring gear 46.

FIG. 4 shows a schematic side view of forming assembly 10 in which the roll axis 34 is shown angularly offset relative to the mandrel central axis a, as indicated by angle .theta.. The forming elements 20 each include a forming element
longitudinal axis 48 that is also angularly offset relative to the mandrel central axis a, as also indicated by angle .theta.. The roll axis 34 and the longitudinal axis 48 of the forming element 20 interposed between roll 26 and mandrel central axis a
are generally parallel, so that the radially inwardly directed force being applied to the ring blank 14 by the roll 26, as the roll 26 rotates in the direction of arrow 35 and circumscribes ring blank 14. Each roll 26 rolls along ring blank outer
annular surface 17 in a direction of travel that is generally perpendicular to the axis 48 of each of the forming elements 20 disposed on the mandrel 12 as it is interposed between the roll 26 and mandrel central axis a; and therefore the direction of
travel of the rotating roll 26 is also perpendicular to the longitudinal directions of gear teeth 36 being formed on the ring blank 14. While the roll axis 34 about which the wheel 32 rotates is generally parallel to the forming element axis 48, the
articulating motion of the roll 26 in the directions of arrow 50 is generally parallel to the mandrel central axis a. The resultant ring gear 46 shown in FIG. 6 has provided advantages not known in the prior art relating to formed ring gears due to the
articulating motion and the orientation of the rolls 26. Specifically, no machining is needed to the gear teeth 36 due to the improved filling of ring blank 14 over and between the forming elements 20 on the mandrel 12 by virtue of the parallel axial
alignment between the roll axis 34 and the axis 48 of the forming elements 20 interposed between the roll 26 and the mandrel central axis a. This results in a ring gear 46 having a smooth outer surface and uniform wall thickness also not known to present
gear technology unless a substantial amount of machining is performed. This also facilitates a use of the resultant ring gear 46 in high speed applications such as automotive transmissions. It is further believed that by using a plurality of rolls 26
circumferentially spaced around the ring blank 14 and simultaneously being forced radially inwardly toward the mandrel axis a improves both gear teeth 36 profiles and the uniformity of the thickness of the resultant gear 46.

The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, wherein reference numerals are merely for
convenience and are not to be in any way limiting, the invention may be practiced otherwise than as specifically described.